EXCEPTION HANDLING. Resources. [1] Object Oriented Programming with C++
(3rd Edition). E Balagurusamy. [2] Teach Yourself C++ (3rd Edition) H Schildt ...
EXCEPTION HANDLING Resources [1] Object Oriented Programming with C++ (3rd Edition) E Balagurusamy [2] Teach Yourself C++ (3rd Edition) H Schildt
EXCEPTIONS Exceptions are run time anomalies or unusual conditions that a program may encounter during execution. Conditions such as
Division by zero Access to an array outside of its bounds Running out of memory Running out of disk space
It was not a part of original C++. It is a new feature added to ANSI C++.
EXCEPTION HANDLING
Exceptions are of 2 kinds
Synchronous Exception: Out of rage Over flow
Asynchronous Exception: Error that are caused by causes beyond the control of the program
Keyboard interrupts
In C++ only synchronous exception can be handled.
EXCEPTION HANDLING (CONT…)
Exception handling mechanism
Find the problem (Hit the exception)
Inform that an error has occurred (Throw the exception)
Receive the error information (Catch the exception)
Take corrective action (handle the exception)
EXCEPTION HANDLING MECHANISM
It is basically build upon three keywords Try Throw Catch
try block Detects and throws an exception
Exception object catch block Catch and handle the exception
EXCEPTION HANDLING MECHANISM (CONT…)
The keyword try is used to preface a block of statements which may generate exceptions.
When an exception is detected, it is thrown using a throw statement in the try block.
A catch block defined by the keyword ‘catch’ catches the exception and handles it appropriately.
The catch block that catches an exception must immediately follow the try block that throws the exception.
// Block of statements // which detect and // throws an exception // catch exception // Block of statement // that handles the // exception
EXCEPTION HANDLING MECHANISM (CONT…)
Exceptions are objects used to transmit information about a problem.
If the type of the object thrown matches the arg type in the catch statement, the catch block is executed.
If they do not match, the program is aborted using the abort() function (default).
[E.B.] Program 13.1
EXCEPTION HANDLING MECHANISM (CONT…)
Often, Exceptions are thrown by functions that are invoked from within the try blocks.
The point at which the throw is executed is called the throw point.
Once an exception is thrown to the catch block, control cannot return to the throw point.
[E.B.] Program 13.2
EXCEPTION HANDLING MECHANISM (CONT…) Invoke function
throw point
try block
catch block
Function that causes an exception
Invokes a function that contains an exception
Catch and handle the exception
Throw exception
THROWING MECHANISM
The throw statement can have one of the following 3 forms throw(exception) throw exception throw //used to re-throw a exception
The operand object exception can be of any type, including constant.
It is also possible to throw an object not intended for error handling.
THROWING MECHANISM (CONT…)
Throw point can be in a deeply nested scope within a try block or in a deeply nested function call.
In any case, control is transferred to the catch statement.
CATCHING MECHANISM The type indicates the type of exception the catch block handles. the parameter arg is an optional parameter name. The catch statement catches an exception whose type matches with the type of the catch argument.
catch(type arg) { … … … }
CATCHING MECHANISM (CONT…)
If the parameter in the catch statement is named, then the parameter can be used in the exception handling code.
If a catch statement does not match the exception it is skipped.
More than one catch statement can be associated with a try block.
When an exception is thrown, the exception handlers are searched in order for a match.
The first handler that yields a match is executed.
If several catch statement matches the type of an exception the first handler that matches the exception type is executed.
[E.B.] Program 13.3
CATCHING MECHANISM (CONT…)
Catch all exception catch (…) { // statement for processing // all exception }
[E.B.] Program 13.4
RETHROWING AN EXCEPTION
A handler may decide to rethrow the exception caught without processing it.
In such a case we have to invoke throw without any arguments as shown below
throw;
This causes the current exception to be thrown to the next enclosing try/catch sequence and is caught by a catch statement listed after the enclosing try block
[E.B.] Program 13.5
SPECIFYING EXCEPTION
It is possible to restrict a function to throw certain specific exceptions by adding a throw list clause to the function definition.
type function(arg-list) throw(type-list) { ……… ……… ……… } [E.B.] Program 13.6
SPECIFYING EXCEPTION (CONT…)
The type-list specifies the type of exception that may be thrown.
Throwing any other kind of exception will cause abnormal program termination.
If you want to prevent a function from throwing any exception, you may do so by making the type-list empty.
LECTURE CONTENTS
[1] Object Oriented Programming with C++ (3rd Edition) E Balagurusamy
Chapter 13 (Full)
[2] ] Teach Yourself C++ (3rd Edition) H Schildt
Examples only Study the examples from both books carefully
